Accompanying recent popularization of computers, an inkjet printer is widely used for printing letters or drawing an image on paper, film, cloth or the like not only at offices but also at homes.
The inkjet recording method includes a system of jetting out a liquid droplet by applying a pressure from a piezoelectric element, a system of jetting out a liquid droplet by generating a bubble in the ink under heat, a system of using an ultrasonic wave, and a system of jetting out a liquid droplet by suction using an electrostatic force. The inkjet recording ink used therefor includes an aqueous ink, an oily ink and a solid (fusion-type) ink.
Among these inks, an aqueous ink is relatively superior to oily ink or solid (fusion-type) ink in view of production, handleability, odor, safety and the like and therefore, is predominating as the inkjet recording ink at present.
The coloring matter used in such an inkjet recording ink is required to have high solubility in a solvent (ink medium), enable high-density recording, provide good color hue, exhibit excellent fastness to light, heat, air, water and chemicals, ensure good fixing to an image-receiving material and less bleeding, give an ink having excellent storability, have high purity and no toxicity, and be available at a low cost.
However, it is very difficult to find out a coloring matter satisfying these requirements in a high level. Among these requirements, good color hue and excellent fastness are conflicting in many cases and regarding the coloring material for magenta or cyan ink, a coloring matter satisfying the above-described requirements, particularly a coloring matter satisfying both good magenta or cyan color hue and light fastness high enough to withstand the oxidative atmosphere, can be hardly obtained.
Accordingly, although various dyes and pigments for use in inkjet recording have been already proposed and are actually used, a coloring matter satisfying all of the requirements described above is not yet found out at present.
Conventionally well-known dyes and pigments having a color index (C.I.) number can hardly satisfy both color hue and fastness required of the inkjet recording ink.
As for the dye capable of improving the fastness, azo dyes derived from an aromatic amine and a 5-membered heterocyclic amine have been proposed in Patent Document 1. However, these dyes have a problem of bad color reproducibility due to undesirable color hue present in the yellow and cyan regions.
Patent Documents 2 and 3 are disclosing an inkjet recording ink with an attempt to satisfy both color hue and light fastness. However, in use as a water-soluble ink, the coloring matters used in these patent publications are insufficient in the solubility in water. Also, when the coloring matters described in these patent publications are used as a water-soluble ink for inkjet recording, there arises a problem in the fastness to humidity and heat.
In order to solve these problems, compounds and ink compositions described in Patent Document 4 have been proposed. Furthermore, an inkjet recording ink using a pyrazolylaniline azo dye for improving the color hue and light fastness is described (Patent Document 5). However, these inkjet recording inks all are insufficient in the color reproducibility and fastness of the image output.
It has been also found that when an image is recorded on an inkjet special glossy paper for photographic image quality and put on a wall in a room, the image sometimes exhibits extremely bad preservability. The present inventors assume that this phenomenon is ascribable to some oxidative gas in air, such as ozone. This phenomenon scarcely occurs when the air flow is shut out, for example, by putting the image in a glass-made frame, but in this case, use conditions are limited.
This phenomenon is outstanding particularly in the case of inkjet special glossy paper for photographic image quality and raises a large problem for current inkjet recording systems where one of important characteristic features is the photographic image quality.
Furthermore, the aqueous ink is found to readily putrefy and cause a problem that when the ink is aged for a long period of time, the ejection property is seriously worsened due to putrefaction. It is also found that when a single antiseptic is used, the tolerance of bacteria increases and the effect is disadvantageously less expressed.